1. Field of the Invention
The present invention relates to an exposure device, more particularly, to a charged particle beam exposure device using a charged particle beam such an electron beam or an ion beam.
The charged particle beam exposure device having a block mask, which applies a block exposure method, is used to select one or more minute opening patterns from a plurality of opening patterns (block patterns) formed on the block mask and to irradiate a charged particle beam onto a surface of a substrate which is a semiconductor wafer to be processed.
2. Description of the Related Art
Recent developments in the electron beam exposure method have led to an increased use thereof as a method producing the miniaturized patterns required when manufacturing a high density integrated circuit. Further, an ion beam exposure method has been studied, and the ion beam exposure method can form finer patterns because a scattering in a resist film and a reflection from a substrate of the ion beam exposure method are smaller than that of the electron beam exposure method.
Note, in the electron beam exposure method as mainly used in the prior art, for example, an electron beam having a rectangular sectional shape is scanned and irradiated onto a semiconductor wafer to form specific required patterns. Namely, the specific required patterns are obtained by combining each one shot pattern formed by the rectangular shaped electron beam by each one shot operation. Therefore, an area of the one shot operation should be made small, to meet the need for a miniaturization of the required patterns, and thus the number of shot operations required for a unit area becomes large, and accordingly, the throughput of an exposure process is lowered. To solve these problems, a block exposure method has been provided (for example, with reference to H. C. Pfeiffer et al., IEEE Trans. on Electron Devices, Vol. ED-26 (1979) 663).
Namely, a semiconductor integrated circuit requiring an ultra fine pattern, e.g., 64 M-bit or 256 M-bit DRAM, includes an exposure area where in one or more types of block patterns (basic patterns) formed on a block mask are repeatedly selected and exposed. Note, a shape of each of the block patterns is complex, and a size thereof is miniaturized to be included in a sectional area of a variable rectangular beam. Therefore, if such a block pattern is obtained by a one shot operation, the throughput of the exposure process can be raised. Note, in the block exposure method, the basic patterns (block patterns), which are repeatedly used, are performed on a mask (block mask) as a required number of opening patterns, one or more minute opening patterns are selected therefrom, and the selected opening pattern is used for the one shot operation of an electron beam to thereby form a required pattern on a substrate (semiconductor wafer).
Note, the block mask including a plurality of block patterns is made, for example, of silicon or metal, and a thickness of the center portion where in the block patterns of the block mask are formed is about 10 .mu.m. Further, as described above, different minute block patterns formed on the block mask are selected, and then the charged particle beam shaped by each selected block pattern is successively impinged on to the different positions of the substrate.
In the above described charged particle beam exposure device (block exposure device), during a period for inputting exposure data to the exposure device, a period for transferring the input data, or a period for changing the substrate (semiconductor wafer), the charged particle beam exposure device is adjusted to a specific condition to thus immediately start the exposure operation after the elapse of the above periods. Note, a waiting period caused by a change of the substrate is, for example, more than several dozens of seconds, and further, a waiting period for inputting or transferring exposure data to the exposure device is, very long for example, several dozens of minutes. During these periods, a part of the block mask is continuously irradiated by the electron beam, and therefore, a temperature of a part of the block mask is increased and a warping of the opening pattern is caused by the resultant thermal nonuniformity, and further, a contamination of the block mask is caused by a deposition of the polymerizing materials.
Namely, when the charged particle beam is continuously irradiated onto an area of a block pattern of the block mask, the area including the block pattern having a thickness of about 10 .mu.m may become bent, and a part of the block pattern may be melted and eliminated. Further, when the charged particle beam is continuously irradiated onto an area of the block mask, contamination occurs at the irradiated area. Note, the contaminating materials are generally insulating materials, and an electro-static charge is trapped in these contaminating materials, and thus the charged particle beam passing through the block pattern of the block mask may be curved by the electro-static charge of the contaminating materials. Further, the contaminating materials are also produced on a diaphragm aperture unit provided between the block mask and the substrate, and the charged particle beam passing through the diaphragm aperture unit also may be curved by these contaminating materials of the diaphragm aperture unit. These problems will be explained in detail with reference to FIGS. 1 to 3B.